Personal weblog of Ted Pavlic. Includes lots of MATLAB and LaTeX (computer typesetting) tips along with commentary on all things engineering and some things not. An endless effort to keep it on the simplex.

Saturday, July 07, 2007

Breathing is carbon neutral, asshole

The carbon in the carbon dioxide that you exhale is a product of cellular respiration inside your cells. It comes from breaking down sugar (a carbohydrate). The process liberates the carbon from the sugar so that it can bond with the oxygen that you inhale to form carbon dioxide and water (e.g., urine or "pee"), and this releases energy since carbon would much rather be a part of carbon dioxide than sugar. This energy is what you use to go about your day and say statements like the above.

So where does the sugar come from? It what is produced in the photosynthesis that goes on in plants. Photosynthesis uses energy from the sun to reshuffle water and carbon dioxide into oxygen and sugar.

That's right. The carbon you exhale comes from sugar that could not have been made without pulling carbon out of the air.

This is also why combustion, which is related to cellular respiration, of pure biofuels (hydrocarbons) is POTENTIALLY carbon neutral (see notes about sustainable yeilds); the carbon in those fuels was originally pulled out of the air by a plant somewhere, and hopefully more plants will pull it out of the air after combustion. Of course, there are lots of other things involved in combustion (e.g., processing and transporation of biofuels as well as the consumption that goes on in the process of burning those fuels) that are not carbon neutral (and, again, there's that issue of burning so many plants that you don't have any left to take the carbon out of the air; again, see sustainable yield).

You should consider these things when you think about livestock as well. Breathing does not prevent something from being carbon neutral.

So what isn't carbon neutral? If you are releasing carbon that did not (recently) come from a plant source, you are probably not being carbon neutral. Burning fossil fuels is liberating carbon that has been buried for (hundreds of) millions of years. This is why the word fossil is used. This carbon would have stayed buried if it was not for human intervention. This causes a stability problem on the surface of the earth. The carbon cycle gets out of whack because that extra carbon does not go back to its source. In fact, the only way to get that carbon back to where it came from is to have a mass extinction and then millions of years of geological processes.

12 comments:

In short, unless you're metabolizing fossil fuel, then yes. The long story involves a comparison of flow rate.

Aside: Most of the gas in flatulence comes from air packed within food, and so there's no new contribution there. Any other contribution comes from a natural source that at one point took such things out of the atmosphere. The cycle is not typically as clear, but it's there.

Aside: Many people make the mistake that cud chewers (i.e., ruminants, like most of the hoofed ungulates you picture on a farm) release greenhouse gasses (including methane) from their mouths, not their rear ends.

All of these biological processes are "neutral" provided that you're not destroying the extractors faster than you're creating the injectors. That is, churning all of the biomass (including producers, like plants) in the world into consumers (e.g., human beings) is a major carbon problem... you don't have anything left to take the new carbon back out of the atmosphere.

While methane (such as from flatus) is a more potent greenhouse gas than carbon dioxide, it lasts only a few years in the atmosphere.

Methane is also produced by rotting vegetation. If the land used for grazing ruminants weren't used for grazing ruminants, how much of it would be supplanted by rotting wild vegetation, producing the exact same amount of methane? You could grow a forest there, sure - but once it matured, it would be dying & rotting exactly as fast as it was growing.

Surely to reduce the methane produced by ruminants, then, existing grazing land would have to be converted to desert, so as not to produce any greenhouse gases at all. I suppose this would also be beneficial to the cause by virtue of its higher albedo.

I hereby propose a new pro-desertification movement to save the world from farting cows and rotting plants. How does that sound?

Anonymous, so you think the world would be better without people who are different than you,aside from the pollution problem???? I suppose only you narrow-minded jerks should be allowed to exist in this world. If it weren't for you I think our planet would not be polluted at all.

I'll take the AGW movement seriously when they start creating proposals for re-sequestering carbon dioxide instead of eliminating fossil fuels. A nice project to grow and harvest more trees, so the carbon used to make the wood gets sequestered into some nice McMansions for our expanding population, would be a start.

Oh, but then you're increasing the capacity of the planet to support human life, and that's a BAD THING. You can see the real agenda in what the AGW movement doesn't support, as well as what it does.

Anonymous, where is the room for these additional trees that you want to grow when you're also building housing for an expanding population?

Additionally, there is only a finite amount of biomass available. It is certainly not ecologically feasible to have a monoculture of human beings (and... pine trees, in your utopia?), and even if it was, those human beings would have to start eating themselves just to produce more human beings.

I think you misunderstood. It's not photosynthesis that goes on in you; its cellular respiration. Your breathing brings in the oxygen for cellular respiration, which is the animalistic dual of photosynthesis in plants. They complement each other. Plants create sugar (and oxygen) from water, carbon dioxide, and sun using photosynthesis, and you create carbon dioxide and water from the sugar (and oxygen) which gives you the energy that came from the sun.